1. Field of the Invention
The present invention relates to a sensor having a cantilever. More particularly, it relates to a sensor which is designed for use in a device for measuring the thickness of a thin film being formed by a PVD method or a CVD method, or in a vacuum gauge for detecting the intensities of molecular beams being applied to an object, and in which a minute displacement of a cantilever is detected in the form of changes in the tunnel current supplied to the probe of an STM or that of an AFM, or in the form of changes in an atomic force.
2. Description of the Related Art
In the case of the film thickness measuring device, multiple reflection interference, crystal oscillator and the other manners are usually employed as the method for measuring the thickness of a thin film.
According to the multiple reflection interference manner, the film thickness measuring plate, the half of the surface of which has been masked, is arranged adjacent to a sample and thin film forming and not forming areas are formed adjacent to each other on the plate at the time when a thin film is to be formed on the surface of the sample. A metal film having a high reflection rate is uniformly formed all over the plate and a semitransparent film is placed on the plate at an angle of 8. When homogeneous light having wave-length .lambda. is radiated onto the plate in such a way that it is substantially perpendicular to the surface of the plate, linear interference fringes which are shifted from each other at the stepped portion on the surface of the plate by distance (b) are created parallel to each other with interval (b) interposed between them. Therefore, film thickness (d) can be obtained as follows: d=(.lambda./2).multidot.(b/a). In this case, however, the measurement of film thickness is possible only after the thin film is formed on the plate. Therefore, film thickness cannot be measured while forming the thin film on the plate. In addition, it is needed that the thin metal film having high reflection rate is formed on the plate and this makes the measurement for film thickness quite troublesome. When film thickness is smaller than 20-30 .ANG., measurement error becomes quite large, thereby making it impossible to carry out the practical measurement of film thickness.
In the case of the film thickness measurement according to the crystal oscillator manner, the crystal oscillator plate is located adjacent to a sample when a thin film is to be formed on the sample. Film thickness can be obtained by measuring the eigenfrequency of the oscillator plate which changes depending upon the thickness of the film formed on the oscillator plate. However, the temperature of the crystal oscillator plate rises while the thin film is being formed and this causes the frequency of electrical oscillation to be shifted, with the result of making measurement accuracy low.
Molecular beam flux radiated on the processed surface of the sample to form a thin film is not uniform in its strength distribution but its strength is gauss-distributed along the direction passing through the center of molecular beam flux. The strength of molecular beam is high in the center of beam-radiated area but low at the periphery of the area. The developing speed of the thin film becomes therefore slightly different at various parts on the processed surface of the sample and this makes it important to previously know the strength distribution of molecular beam flux radiated on the processed surface of the sample.
The strength distribution of molecular beam is obtained from the regional strengths of the beam which are measured at predetermined areas in a plane perpendicular to the beam flux and including the axis of the beam flux. The regional strengths are measured by regional vacuum gages and they are obtained from momentums of molecular beam measured at predetermined areas on the processed surface of the sample by ion gages. The surface ionization gage and detector of the electrons collision type are usually used as the ion gage. The surface ionization gage and electrons collision type detector have openings only in the direction of incident molecular beam, ionize gas molecules passed through the openings and measure the momentum of molecular beam from the equilibrium pressure of gas in the detector obtained by measuring ionization current flowing while gas molecules are being ionized. In the case of the surface ionization gage and electrons collision type detector, however, it is needed for the detection of ion current that the opening through which molecular beam enters has a diameter of at least 10 mm. This makes the resolution, at which the detector can detect the strength distribution, quite low. It is therefore difficult to measure the strength distribution of molecular beam in the space. Further, the pressure of molecular beam measured by the ion gage is likely to be influenced by remaining gas except the molecular beam.